The present invention relates to viscometers that are usable in situ in large reaction vessels for real time measurement of viscosity of liquids while undergoing chemical reaction or like process conditions.
The art of viscosity measuring has many products for laboratory or industrial off-line measurement of samples and a few for in-line (e.g. in piping or small vessels) measurement, e.g. the TT200 Process Viscomcter of Brookfield Engineering Laboratories, Inc., which has a viscosity range of 10-500,000 cps, shear rate range of 1 to 1,000 sec. .sup.-1, and a pressure range of 0-200 psi. However, it has a working end length on the order of one foot. There is a need for a viscosity measuring instrument that can be mounted on a standard access port flange and inserted into a reaction vessel (e.g. for polymerization, cooking or boiling, compounding, mixing, thickening, solvating, saponification, reduction, etc.), with a working end of the instrument within the vessel substantively in excess of three feet, typically in the five to fifteen foot range.
It is an object of the invention to meet the foregoing needs and at the same time meet requirements of: (a) being top-mountable or side-mountable on reactor vessels; (b) withstanding high side loading against spindle and shaft; (c) having very low maintenance requirements; (d) withstanding vessel cleanings while installed; (e) being easily clearable while in the vessel (i.e. no special purge fittings and the instrument being clearable as the inside of the vessel is flushed); (f) withstanding all vessel operating conditions (temperature, pressure); (g) being suitable for explosion proof applications; (h) being easily removable from the vessel even when the length of the instrument's working end is on the order of ten to twelve feet long; (i) being fail-safe to prevent parts from falling into the vessel ( e.g., due to an overtorque situation); (j) being highly sensitive to viscosity changes during reaction; (k) being extremely repeatable under the same operating conditions; and (1) maintaining accuracy under all process operating conditions.